The present invention relates to the production of internegatives from transparencies and, more particularly, to apparatus for producing internegatives in which the resulting internegative is optimally exposed to the original image and corrected for contrast as part of the exposure process.
In order to produce a photoprint of a transparency, the conventional practice is to illuminate the transparency from the rear and photograph the back-illuminated transparency with a conventional camera. The exposed film is then developed to yield a negative, viz., the internegative, which is then used to produce a photographic print.
While various types of equipment have been developed for the purpose of exposing an internegative as part of the above-described process, a typical arrangement uses an illuminated copy table upon which the slide transparency is placed and through which light from the underlying table passes. A conventional camera, typically equipped with a bellows and lens, is mounted above the copy table so as to allow photographing of the image presented by the back-illuminated slide. A specially designed `internegative` film, which has a lower contrast than conventional films, is used, and filters must be provided with the light source to correct for undesired spectral components in the illumination. The low-contrast internegative film is required since the process of effecting a photograph of the back-illuminated transparency with normal film increases the contrast of the resulting image; the low-contrast internegative film thus functions to compensate for this effect. When conventional contrast films are used, the increased-contrast effect results in a loss of detail in the resulting image, particularly in the shadow and highlight areas of the image. If conventional film is used, the contrast can be lowered by a second exposure to a minute, but calculated, quantity of diffuse light energy which has the effect of slightly fogging the resulting image and reducing the undesired increment in contrast. In this latter situation, the camera operator must first determine the parameters for the initial exposure of the image, effect the exposure, determine the parameters the contrast-correcting exposure, and then effect the second exposure.
As can be appreciated, the equipment and process steps described above are quite involved and require a fair degree of skill on the part of the operator. In those situations where conventional contrast film is used and contrast correction is effected by another exposure to a source of diffuse light, considerable care must be exercised to avoid overexposure of the image and an unacceptable internegative. In an effort to maximize the probability of an acceptable internegative, many exposures at differing aperture settings and exposure times must be made so that at least one of the resulting internegatives is satisfactory. This practice, of course, is inefficient from the standpoint of time and cost.